Hypersaline Lake Research Articles

A diatom-based predictive model for inferring past conductivity in Chadian Sahara lakes

For decades, diatoms have been recognized as powerful bio-indicators of modern water quality. They have also been utilized in the design of transfer functions, which can be applied to diatom assemblages in lake sediment cores to infer aspects of past lake hydrochemistry and estimate variables that can be incorporated into paleohydrology models. The Ounianga lakes, in the heart of the Chadian Sahara, possess unique and well-preserved sediment records that extend back beyond the middle Holocene. Today, the lakes display a range of hydrochemical conditions, from fresh to hypersaline. Mainly fed by fossil groundwater that originates in the Nubian Sandstone Aquifer System, measured conductivity across these lakes varies from 217 to 352,000 µS cm−1, values that are influenced by factors such as hydrology, local geomorphology (e.g., depth and area), and aquatic vegetation. Although these lakes have been on the UNESCO World Heritage List since 2012, they have never been studied in detail because they are located on the fringes of the Chadian Sahara. The distribution of diatom taxa in the lakes today is closely linked to water-column physical and chemical conditions, especially conductivity. Whereas each lake has particular features that influence its diatom flora, diatoms across a conductivity gradient enabled identification of three distinct waterbody types, freshwater lakes, meso-saline to hyper-saline lakes, and freshwater springs. Relationships between diatom species distributions and environmental variables were examined using multivariate analysis, which revealed that conductivity is the variable that explains most of the variance in the diatom flora. We used modern diatom assemblages from the lakes to develop a predictive model (transfer function) for conductivity, using the weighted averaging method. Our conductivity prediction model is strong, with a coefficient of determination (R2) of 0.89 between estimated and measured values, and a value of 0.78 using jackknife estimates of prediction. This study better constrained conductivity optima and tolerance values for diatom species found in the Ounianga lakes, thereby enabling development of a model that will yield better inferences for past conductivity, using diatoms from lake sediment records in the region.

Unraveling an alkaline lake and a climate change in Northeastern Brazil during the Late Aptian

The Codó Formation is an Aptian marine-influenced lacustrine depositional system in the Parnaíba Basin (Brazil). This unit is an important sedimentary succession because of the high organic matter content and for being an ancient analog for the depositional systems of the Brazilian Pre-salt interval. However, mineralogical and lithogeochemical studies have not been sufficiently carried out on the Codó Formation, which hinders detailed sedimentological knowledge. We report new mineralogical and lithogeochemical data that allow a better understanding of the environmental, climatic, and provenance evolution of the Codó deposits. Mineralogical and lithogeochemical studies were performed on 50 lutite samples collected from the 1-UN-32-PI core and 13 outcrop lutite samples obtained from sites close to the Grajaú and Imperatriz regions. A magnesium-sulfate-rich shallow alkaline hypersaline lake was identified in the lower Codó Formation based on the identification of a clay mineral assemblage composed of authigenic saponite and detrital illite. Hydrothermal processes were interpreted as the magnesium source of this alkaline lake. A salinity-alteration event was identified at the upper limit of the alkaline lake and was interpreted as the first marine ingression in the Codó Formation. This event changed the lake's pH from alkaline to acid, inhibiting the formation of Mg-smectites, and changing its hydrochemical conditions, originating a marine-influenced sulfate-rich acid saline/hypersaline sabkha. This facies succession coincides with a clay mineral assemblage composed of detrital montmorillonite, illite and kaolinite. A regional paleoclimate humidification process was identified from the sabkha to a lagoon facies succession in the upper Codó Formation. This last succession reveals the marine-dominated interval of the Codó Formation and coincides with a clay mineral assemblage composed of detrital kaolinite, montmorillonite and illite. Based on lithogeochemical data, a common post-Archean intermediate source area was also interpreted for these three environments.

Evaporation from the dried-up lake bed of Lake Urmia, Iran

Lake Urmia in north-western Iran was once one of the world's largest hyper-saline lakes and represented a unique ecosystem for a number of endangered species. The lake's shrinking over the past decades has attracted considerable attention and several studies have addressed its water balance. Yet, evaporation of shallow groundwater from the dried-up lake bed has not been fully quantified – despite the appreciable size of these areas (approx. 4000 km2 in summer 2015).Here, we target this water cycle component by combining column experiments with upscaling and regionalisation techniques. In the experiments, we studied evaporation from two undisturbed soil cores from the exposed lake bed in a climate chamber, mimicking diurnal temperature and humidity variations in the three summer months of the study area. Despite the dropping water levels in the columns and the formation of salt crusts, evaporation rates remained remarkably constant (0.12 and 0.20 mm d−1). This suggests that the system is not driven by slow vapour diffusion, but controlled by capillary rise in the fine-grained sediments, ensuring steady water supply to the column surface. Thus, evaporation from the dried-up lake bed can be assumed to be largely independent from the unsaturated zone thickness (within the observed water level range) and evaporation rates can be simply upscaled and regionalised by considering the satellite-derived development of dried-up lake bed areas (1998–2020).In this time-period, estimated summer evaporation from the exposed lake bed reached maximum values of 0.04 and 0.07 km3 (summer 2015). While these absolute numbers are significant (comparable to the catchment's annual urban drinking water consumption), they correspond to only 4 and 7 % of the evaporation from the open lake surface (1.06 km3).

Spatio-Temporal Variations in the Geochemistry of Laguna Salada de Chiprana, NE Spain

Hypersaline lakes are sensitive and increasingly threatened ecological and depositional environments that are host to a diverse spectrum of industrial services, natural resources, and environmental processes. Furthermore, they are also important repositories of high-resolution palaeoenvironmental information and are potentially key archives in the reconstruction of environmental, climatic conditions and past human impacts in areas where other such repositories may not be available. Many saline lakes are threatened by increased farming and irrigation practices and the effects of global warming. Geochemical XRF analyses of a transect of sediment cores from Laguna Salada de Chiprana, a permanent hypersaline lake in the Iberian Peninsula, provide insights into geochemical processes and palaeoenvironmental changes occurring at the site throughout the last 300–400 years. Key changes identified within the sequence are defined both from a spatial and temporal aspect and characterise the profundal and littoral sub-environments of the lake. Initially, the onset of a phase of widespread agriculture and irrigation in the region occurred in the late 16–17th century to ~1850AD and was associated with relative increases in lake levels. This was followed by decreasing lake levels between 1850 and 1950AD, likely associated with increasing evaporative processes and decreased irrigation returns to the lake, which also allowed for increased organic productivity in the profundal setting. This may have been associated with the transition of the site to a wetland-type setting, where biological processes were able to flourish in the shallower central depocentres of the lake. In sequence, the introduction of farm machinery and changing irrigation patterns occurred around 1950, causing small increases in lake levels, colonization by charophytes as well as increased organic productivity in the littoral setting, likely due to the establishment of suitable environments for biological processes to occur in the shallower margins of the lake when water levels rose. From this period to the present day, slow drawdown of the lake has occurred coupled with increasing management of the site by the regional government, leading to several phenomena. Evaporative processes are high throughout the lake; there are falling but highly variable water levels and there is a segmentation of organic productivity, whereby falling lake levels permit increased organic productivity in the profundal setting but decrease productivity in the littoral setting due to the establishment of harsh evaporitic and erosive conditions in this area. The reconstruction reveals the high sensitivity of Lake Chiprana as an environmental archive and illustrates the need to utilise multiple sediment cores for accurate palaeoenvironmental reconstructions of saline lakes due to the strong variability in depositional and geochemical sub-environments.

An Ecological Expert System Optimization for Assessing Environmental Water Requirements of Hypersaline Lakes

The present study proposes an applicable methodology to optimize environmental water requirement of hypersaline lakes with a focus on Urmia lake as the case study in which remote sensing analysis, machine learning model and fuzzy expert system are linked. A machine learning model was developed to simulate effective abiotic parameters in which bands of operational land imager (Landsat 8) were inputs and depth and total dissolved solids were the outputs of the model. Moreover, an ecological expert system using Mamadani fuzzy inference system was developed to generate the habitat suitability map for the selected target species. Then, a multivariate linear model was developed to assess unit habitat suitability in which water level and total inflow of the lake were the variables of the model. An optimization model was developed to assess environmental water requirement in which habitat suitability between natural and regulated flows and water supply loss was minimized. The multivariate linear model was applied to assess habitat suitability in the optimization model. Based on the results in the case study, the proposed combined model is able to balance the ecological requirements and water demand by allocating 60% and 40% of total inflow to environmental water requirement and water demand respectively. Average habitat loss proposed by the optimal environmental water requirement was less than 20% which implies the robustness of the model. Generating habitat suitability maps of the lake by a reliable method which is used in the environmental flow optimization might be the significance of the proposed method.

Water and productivity accounting using WA+ framework for sustainable water resources management: Case study of northwestern Iran

An exhaustive evaluation of water resources is a prerequisite for evidence-informed planning and implementing sustainable management strategies. However, the lack of sufficient information on water supply and consumption, alongside the technical limitations on comprehensive accounting for inter-relations and interactions between the subsystems, has resulted in decisions with often long-lasting outcomes and undesirable consequences. Water accounting is a tool for systematic acquisition, analysis, and reporting of water-related information to fill the existing knowledge gap on water flows and fluxes. In this study, Water Accounting Plus (WA+) framework is applied to the western region of Lake Urmia, a dying hyper-saline lake, to assess water use and crop water productivity (CWP) from 2010 to 2016. Remotely sensed information along with a distributed hydrological model (SPHY) is used to fill the information gap on water resources and inform effective policy actions. Our analysis reveals that the agricultural sector is neither productive nor efficient while there is a considerable scope to ameliorate water productivity and beneficial water use by adopting proper water management practices. Average CWP values for wheat, sugarbeet, vineyard, and apple vary between 0.38 and 0.55, 5.1–5.6, 1.5–1.7 and 1.9–2.3 (kg/m3), respectively while storage changes show consistent depletion, especially during dry year, up to 117 MCM. The results indicate that a 40% reduction in blue water use is achievable to supply additional water to revive Lake Urmia. This study highlights the importance of water accounting and information flow for decision-makers, practitioners, and farming communities to define practical targets and enhance productivity in water-scarce regions.

Brackish and Hypersaline Lakes as Potential Reservoir for Enzymes Involved in Decomposition of Organic Materials on Frescoes

This study highlights the decomposing role through the hydrolytic activities of fungi isolated from natural environments represented by brackish and hypersaline lakes in Romania. Novel strains belonging to the Penicillium, Aspergillus, and Emericellopsis genera were isolated and screened for the ability to produce extracellular hydrolytic enzymes, i.e., proteases, lipases, amylases, cellulases, xylanases, and pectinases. According to salt requirements, they were classified as moderate halophilic and halotolerant strains. Agar plate-based assays with Tween 80, slide cultures with organic deposits, and quantitative evaluation allowed the selection of Aspergillus sp. BSL 2-2, Penicillium sp. BSL 3-2, and Emericellopsis sp. MM2 as potentially good decomposers of organic matter not only in lakes but also on deposits covering the mural paintings. Experiments performed on painted experimental models revealed that only Penicillium sp. BSL 3-2 decomposed Paraloid B72, transparent dispersion of casein, beeswax, sunflower oil, and soot. Moreover, using microscopic, spectroscopic, and imaging methods, it was proved the efficiency of Penicillium sp. BSL 3-2 for decomposition of organic deposits artificially applied on frescoes fragments.

The Prawn Palaemon adspersus in the Hypersaline Lake Moynaki (Crimea): Ecology, Long-Term Changes, and Prospects for Aquaculture

For several years, the prawn Palaemon adspersus population was studied in a hypersaline lake (Crimea) for the first time. P. adspersus is a more halotolerant species than previously thought and can survive and breed up to a salinity of 55 g/L and probably higher. A significant positive correlation was found between the number and biomass of the prawns and the seagrass Ruppia shoot density. The spring temperature increase from 5.5 to 24 °C was accompanied by a significant increase in the prawn number (p = 0.001). In the males and females, the spatial heterogeneity of the distribution of prawns significantly (p = 0.005) negatively correlated with the abundance of prawns. In the period from 2018 to 2021, the area of Ruppia cover and the prawn abundance in the lake decreased, and a significant correlation was found between those changes. High salinity, judging by our data, can reduce the production potential of the species, but the absence of predators in Lake Moynaki allowed the prawns to reach a higher abundance than was observed in other habitats. P. adspersus can be successfully cultivated in hypersaline waters with a salinity up to 55 g/L as a perspective object for Integrated Multi-Trophic Aquaculture. The development of aquaculture in hypersaline waters may help to save freshwater resources, and the development of aquaculture in brines formed during the desalination of seawater will make it more economically viable to obtain freshwater from seawater.

Field scale spatio-temporal variability of wind erosion transport capacity and soil loss at Urmia Lake

Urmia Lake has been known as the second hypersaline lake in the world, with the surface area of approximately 5200 km2. With decreasing the water input of the lake due to anthropogenic activities, the susceptible areas to wind erosion and dust emission were extended during the last decades. The present study attempted to measure wind erosion on the edge of Urmia Lake for three years since 2017. In order to provide a quantitative understanding of wind erosion parameters in the dried up Urmia Lake area, and to prioritize different areas in terms of wind erosion intensity, it was necessary to establish wind erosion measurement and monitoring stations in different areas of dried up shores. Wind erosion measurement and monitoring stations were established in six erodible areas such as Salmas, Jabal Kandi, Soporghan, Miandoab, Khaselou and Ajabshir. Wind erosion parameters such as transport capacity and soil loss in the dried margin of Urmia Lake were determined. For this purpose, BSNE traps were used in the layout of two circles having an identical center. After each wind erosion event, sediment traps were emptied and weighted; then, the vertical and horizontal distribution of the particulate matters was calculated. Comparison of the values of maximum transport capacity-fmax (kg/m.yr) and soil loss- SL (ton/ha.yr) of aeolian particulate in 2017 showed that the two main centers of wind erosion on the edge of Urmia Lake were Ajabshir and Jabal Kandi. The stations of Khaselou, Salmas, Soporghan and Mianduab were in the declined ranking. Results showed that the transfer capacity values were 351.97 and 297.30 kg/m/year and soil losses were 18.04 and 35.4 ton/ha/year, respectively, for the stations with high wind erosion potential, i.e., Ajab Shir and Jabal Kandi, in 2017. Furthermore, these values were significantly reduced for the mentioned stations in 2019, so that the values obtained from the transfer capacity reached 54.93 and 40.39 kg/m/year and soil losses reached 3.70 and 2.43 ton/ha. Investigating the results of transport capacity and soil loss showed the decreasing trend in wind erosion rate due to the increasing water level of the lake as well as biological and engineering conservation practices (non-live windbreaks) from 2017 to 2019.

Widespread declines in water salinity of the endorheic Tibetan Plateau lakes

The Tibetan Plateau (TP) hosts more than one thousand lakes (>1km2) in its endorheic basins. The changing climate in recent decades has led to significant modifications in the endorheic hydrologic system. Most TP lakes experienced dramatically expanding areas, rising water levels, and increasing storage, which inevitably influenced the lake salinity. This study provides a regional-scale investigation of water salinity changes of the TP lakes (for 83 lakes with two-epoch salinity records, among the approximately 160 lakes >50km2) by synthesizing multi-source data around the 1970s and 2010s. Our results reveal lake salinity has considerably declined for most expanding lakes across the endorheic basins. The mean salinity of 62 terminal lakes dropped from 92.76 g l−1 to 42.00 g l−1 during the 1970s–2010s, in contrast to the slight variations (3.42 g l−1 to 1.48 g l−1) of the 21 exorheic or upstream lakes. As a result, many hypersaline lakes have become polysaline or oligosaline lakes, such as Cedo Caka, Norma Co, etc. In particular, some large lakes (e.g., Siling Co, ‘Twin Lakes’, and Ayakkum Lake) also experienced significant drops in water salinity, with the exceptional cases for Nam Co and Qinghai Lake probably due to the relatively low ratios of increased water mass to their net storages. The widespread declining water salinities could greatly influence bacterial richness, diversity, and evenness, and affect the aquatic carbon cycle and utilization in the high-altitude endorheic lakes. More attention should be paid on understanding the saline lake ecosystem evolution and the regional carbon cycle in response to changing water salinity of the TP lakes.

Recurring lacustrine depositional successions in the Wilkins Peak Member, Green River Formation

Mineralogy, petrographic textures, and sedimentary structures from the world’s largest trona deposit, the Wilkins Peak Member (WPM) of the early Eocene Green River Formation (GRF), Bridger subbasin, Wyoming, provide key data about depositional conditions and paleoenvironments. The 250 m-long WPM interval in the Solvay S-34-1 drill core analyzed in this study contains a detailed record of sedimentation in the Bridger subbasin at the deepest area of a hydrologically-closed basin during peak Cenozoic atmospheric CO2 concentrations. Large accumulations of trona (Na3(HCO3)(CO3)·2H2O), shortite (Na2Ca2(CO3)3), northupite (Na3Mg (CO3)2Cl), and halite (NaCl; now replaced by trona), occur in the lower half of the WPM. Modern saline lake environments such as Lake Magadi, Kenya, and the Dead Sea, Israel-Jordan, are useful analogues for interpreting paleolake conditions associated with evaporite deposition in the Solvay S-34-1 core. Solvay saline lake deposits are organized into meter-scale shallowing-upward successions, beginning with (1) oil shale overlain by (2) trona, in places interbedded with oil shale, followed by (3) peloidal dolomite grainstone and/or silty dolomitic mudstone, and (4) massive mudstone with disruption features or desiccation cracks, and/or siliciclastic sandstone with ripple cross-stratification. Based on observations of modern hypersaline lake environments, WPM evaporite deposition at the basin depocenter is interpreted to be controlled by inflow water composition and volume, evaporative concentration, and seasonally-driven lake temperature fluctuations, resulting in recurrent patterns in evaporite mineralogies and textures.

Draft Genome Sequence of Virgibacillus sp. Strain AGTR, Isolated from Hypersaline Lake Acıgöl in Turkey.

ABSTRACTVirgibacillus sp. strain AGTR, which is a haloalkaliphilic microorganism, was isolated from a sediment sample collected in hypersaline Lake Acıgöl in Turkey. It has the potential to produce biotechnologically essential proteases. Here, the whole-genome sequence and its annotations are reported.

Natranaeroarchaeum sulfidigenes gen. nov., sp. nov., carbohydrate-utilizing sulfur-respiring haloarchaeon from hypersaline soda lakes, a member of a new family Natronoarchaeaceae fam. nov. in the order Halobacteriales

A pure culture of alkaliphilic haloarchaeon strain AArc-ST capable of anaerobic growth by carbohydrate-dependent sulfur respiration was obtained from hypersaline lakes in southwestern Siberia. According to phylogenetic analysis, AArc-ST formed a new genus level branch most related to the genus Natronoarchaeum in the order Halobacteriales. The strain is facultatively anaerobic with strictly respiratory metabolism growing either by anaerobic respiration with elemental sulfur and thiosulfate as the electron acceptors or by aerobic respiration at microoxic conditions. Thiosulfate is reduced partially to sulfide and sulfite. It is a first sulfur-reducing alkaliphilic haloarchaeon utilizing sugars, starch and glycerol as substrates for anaerobic growth. It is extremely halophilic (optimum at 3.5 M total Na+) and obligately alkaliphilic (optimum at pH 9.5). The dominant polar lipids include PG and PGP-Me with the archaeol (C20-C20) or extended archaeol (C20-C25) cores. The dominant respiratory lipoquinone is MK-8:8. On the basis of unique physiological properties and results of phylogenetic analysis, the soda lake isolate is suggested to be classified into a novel genus and species Natranaeroarchaeum sulfidigenes gen. nov., sp. nov. (=JCM 34033T = UNIQEM U1000T). Furthermore, on the bases of phylogenomic reconstruction, a new family Natronoarchaeaceae fam. nov. is proposed within the order Halobacteriales incorporating Natranaeroarchaeum and three related genera: Natronoarchaeum, Salinarchaeum and Halostella.

Monitoring and Prediction of the Urmia Lake Drying Trend Based on Time-Series Remotely Sensed Images and Artificial Neural Networks

Urmia Lake, which is the second largest permanent hypersaline lake in the world, is shrinking in recent decades. Since accurate spatial information about the lake is essential to managing the current and emerging crises of the lake, this study is used Urmia Lake satellite images time-series to investigate drought trends by analyzing via Artificial Neural Networks (ANN). The proposed approach is comprising the following four steps. First, yearly time-series Landsat images (2000-2022) are corrected geometrically and radiometrically. Then, time-series images of 2000-2020 are classified into five land cover classes, including; deep water, shallow water, salt, soil, and vegetation. In the third step, ANN trained for 2000-2019 as input and tested for 2020 as an output. Finally, the trained ANN is proposed to predict the future land covers of the lake (for 2021 and 2022 years). In order to evaluate the proposed model, the predicted maps of 2021 and 2022 were compared with their corresponding ground truth maps and quantitative criteria were calculated. The overall accuracy of the prediction for 2021 and 2022 is equal to 92.75% and 90.62%, respectively, which indicates the high capability of the proposed method for modeling and predicting changes in Urmia Lake and its shores.

Benthic quality assessment of a hypersaline lake along the southeast coast of India

The study describes macrobenthic community structure for assessing the benthic quality of a hypersaline lake along the southeast coast of India. Sediment and water samples were collected during November 2018 (Northeast Monsoon — NEM), April (Pre-Monsoon — PRM), and July 2019 (Southwest Monsoon — SWM). Based on salinity distribution the lake can be characterized into four regions viz., Northern inlet, Middle inlet, Southern inlet, and Central region. Seasonal analysis showed that the middle inlet and the central region of the lake experience hypersaline conditions throughout the year. Macrobenthic abundance and diversity index were high during SWM compared to other seasons. Some macrobenthic species (Cirratulus filiformis, Pagurapseudopsis gymnophobia, Apseudes chilkensis, Tanais sp.) showed a high preference for non-hypersaline regions while their presence in hypersaline regions was comparatively low/sparse. The present study identified that polychaete species such as Dendonereis aestuarina, Sigambra parva, Capitella capitata, Heteromastus similis can survive in hypersaline (> 60) conditions. The seasonal benthic quality status of the lake assessed by the AZTI Marine Biotic Index (AMBI) indicated heavily disturbed conditions during NEM and slightly disturbed during SWM.

Artemia spp. (Crustacea, Anostraca) in Crimea: New Molecular Genetic Results and New Questions without Answers

Many works have been devoted to the study of the molecular genetic diversity of Artemia in different regions; however, there are regions such as Crimea, the largest peninsula in the Black Sea, which has seen few studies. Artemia specimens from several Crimean hypersaline lakes were analyzed using the mitochondrial marker cytochrome oxidase C (COI). The analyzed individuals from bisexual populations formed clades with the species A. salina, A. urmiana, A. sinica, and A. monica (=A. franciscana). A. sinica and A. monica had not been recorded in Crimea previously. In Lake Adzhigol, the three species A. urmiana, A. sinica, and A. monica were found at the same time, which has not been noted anywhere before. In the Crimean lakes, a total of 10 haplotypes were found, six of them for the first time: Once for A. monica, once for A. sinica, and four for A. salina. Those haplotypes may be regarded as endemic to Crimea. In the 1990s, experiments were carried out in Lake Yanyshskoe using mainly purchased cysts of Artemia, so A. monica and A. sinica were introduced into Crimea and could then have easily been spread by birds to other Crimean lakes.

The effect of salinity on water 17O/16O ratios in brines

Closed-basin lakes respond strongly to climate related changes in their water balance. Lake water isotopic composition can thus serve as a sensitive indicator of paleo-hydrological conditions. Such lakes are often highly saline, so that the effect of salinity on the isotopic composition of lake water has to be accounted for in analyzing lake water evaporation and lake sediment isotopic records. Whereas the effect of salinity on δ18O has been well characterized, this has not been done for the emerging proxy 17Oexcess [Oexcess17=106[ln⁡(10−3δ17O+1)−0.528ln⁡(10−3δ18O+1)]. To this end, we measured for the first time δ17O and δ18O of water in NaCl, CaCl2, and MgCl2 solutions of a wide range of concentrations (1 to 4 molal), using CO2-H2O isotope exchange at 25°C. The results show that although both δ18O and δ17O are sensitive to salinity, 17Oexcess is independent of salinity. Therefore, when analyzing lake water composition, the effect of salinity on δ18O and δ17O has to be accounted for, whereas 17Oexcess remains unchanged. These findings have important implications when studying evaporation in hypersaline lakes and for reconstructions of past water balance in saline closed-basin lakes.

The Sedimentation Rate in the Crimean Hypersaline Lake Aktashskoye Estimated Using the Post-Chernobyl Artificial Radionuclide 90Sr as a Radiotracer

Artificial 90Sr is one of the most important long-lived radionuclides of global radioactive fallout from the atmosphere after the testing of nuclear weapons and the accident at the Chernobyl Nuclear Power Plant in 1986. In addition to fallout from the atmosphere, secondary radioactive contamination of Crimea was mainly from the Dnieper River and the North Crimean Canal, which occurred until 2014. 90Sr was used as the optimal radiotracer for estimating the rate of sedimentation in the Crimean hypersaline lake. Its vertical distribution in the bottom sediments was assessed. In the core of the bottom sediments, the detectable activity of 90Sr in layers 0–1.5 cm and 16.7–21.9 cm was absent, and it was determined again in the layer of 15.5 cm, which was associated with atmospheric fallout of the radionuclide after the Chernobyl NPP accident. There were well-isolated peaks of specific activity in layers at a depth of 4.6 and 13.3–14.3 cm. The calculated rate of sedimentation varied within 0.5–1.5 cm year−1: the minimum rate corresponded to the period 1971–2017, and the highest rate corresponded to the period 1954–1971.

Stratigraphic record reveals contrasting roles of overflows and underflows over glacial cycles in a hypersaline lake (Dead Sea)

In lakes and oceans, links between modern sediment density flow processes and deposits preserved in long-term geological records are poorly understood. Consequently, it is unclear whether, and if so how, long-term climate changes affect the magnitude/frequency of sediment density flows. One approach to answering this question is to analyze a comprehensive geological record that comprises deposits that can be reliably linked to modern sediment flow processes. To address this question, we investigated the unique ICDP Core 5017-1 from the Dead Sea (the largest and deepest hypersaline lake on the Earth) depocenter covering MIS 7-1. Based on an understanding of modern sediment density flow processes in the lake, we link homogeneous muds in the core to overflows (surface flood plumes, ρflow<ρwater), and link graded turbidites and debrites to underflows (ρflow>ρwater). Our dataset reveals (1) overflows are more prominent during interglacials, while underflows are more prominent during glacials; (2) orbital-scale climate changes affected the flow magnitude/frequency via changing salinity and density profile of lake brine, lake-level, and source materials.

Ecology of Methanonatronarchaeia.

Methanonatronarchaeia represents a deep-branching phylogenetic lineage of extremely halo(alkali)philic and moderately thermophilic methyl-reducing methanogens belonging to the phylum Halobacteriota. It includes two genera, the alkaliphilic Methanonatronarchaeum and the neutrophilic Ca. Methanohalarchaeum. The former is represented by multiple closely related pure culture isolates from hypersaline soda lakes, while the knowledge about the latter is limited to a few mixed cultures with anaerobic haloarchaea. To get more insight into the distribution and ecophysiology of this enigmatic group of extremophilic methanogens, potential activity tests and enrichment cultivation with different substrates and at different conditions were performed with anaerobic sediment slurries from various hypersaline lakes in Russia. Methanonatronarchaeum proliferated exclusively in hypersaline soda lake samples mostly at elevated temperature, while at mesophilic conditions it coexisted with the extremely salt-tolerant methylotroph Methanosalsum natronophilum. Methanonatronarchaeum was also able to serve as a methylotrophic or hydrogenotrophic partner in several thermophilic enrichment cultures with fermentative bacteria. Ca. Methanohalarchaeum did not proliferate at mesophilic conditions and at thermophilic conditions it competed with extremely halophilic and moderately thermophilic methylotroph Methanohalobium, which it outcompeted at a combination of elevated temperature and methyl-reducing conditions. Overall, the results demonstrated that Methanonatronarchaeia are specialized extremophiles specifically proliferating in conditions of elevated temperature coupled with extreme salinity and simultaneous availability of a wide range of C1 -methylated compounds and H2 /formate.